Abstract: A visible wavelength InGaP/InGaAlP semiconductor laser diode with a double hetero (DH) structure capable of shortening the wavelength having a compound semiconductor substrate of a first conductivity type; a compound semiconductor first clad layer of the first conductivity type formed over the substrate; an undoped compound semiconductor active layer formed over the first clad layer, the lattice constant of the active layer being different from the clad layer to tensile strain the active layer; a compound semiconductor second clad layer of a second conductivity type formed over the active layer, the lattice constant of the second clad layer is the same as that of the first clad layer; a compound semiconductor current confining layer of the first conductivity type formed over the second clad layer except for a central region such that current in the central region flows parallel to the growth direction; a compound semiconductor cap layer of the second conductivity type formed over the current confining layer;

Abstract: There is disclosed a tensile strained blue-green II-VI quantum well laser. The tensile strained blue-green II-VI quantum well laser comprises of a semiconductor substrate; a buffer layer formed on the semiconductor substrate; a first ZnSe cladding layer formed on the buffer layer; a multi-quantum well layer formed on the first ZnSe cladding layer, consisting of a ZnS.sub.y Se.sub.1-y active region and a Mg.sub.z Zn.sub.1-z S.sub.w Se.sub.1-w barrier region; a current-restricting layer formed on the multi-quantum well layer; a second ZnSe cladding layer formed on the current-restricting layer; and a cap layer formed on the second ZnSe cladding layer. The inventive tensile strained blue-green II-VI quantum well laser is capable of reducing the oscillation wavelength into not more than 500 nm at room temperature and of lowering the threshold current density to as low as 1,000 A/cm.sup.2.

Abstract: A semiconductor laser including an n-type GaAs substrate, an n-type clad layer formed over the substrate, an undoped AlGaAs active layer formed over the clad layer, the active layer having a varying aluminum content depending on the level therein, to form predetermined asymmetric quantum wells, a p-type clad layer formed over the active layer, and a p-type cap layer formed over the p-type clad layer. The active layer has a lower surface constituted by Al.sub.y Ga.sub.1-y As having a low aluminum content and an upper surface constituted by Al.sub.z Ga.sub.1-z As having a high aluminum content, and the aluminum content of the AlGaAs of the active layer present between the lower and upper surfaces increases gradually, while the AlGaAs of both types of the clad layers includes Al.sub.x Ga.sub.1-x As having an aluminum content higher than that of the active layer, to form an asymmetric graded quantum well structure. The AlGaAs of the active layer includes Al.sub.y Ga.sub.

Abstract: A semiconductor laser comprising an active layer in which a biaxial compressive strain is generated, to improve an optical gain. The semiconductor laser has a double-heterostructure comprising an active layer of a (Cd,S)Zn(Se,Te) compound, a pair of cladding layers formed beneath and over the active layer and made of a Zn(Se,Te) compound, and a pair of strained layers formed among the active layer and the cladding layers and made of a (Cd,S)Zn(Se,Te) compound. The strained layers is comprised of a Group II-VI compound semiconductor having lattice constants smaller than and band gaps larger than those of the active layer so that a biaxial compressive strain is induced in the active layer, thereby enabling the optical gain to be improved. It is possible to provide semiconductor lasers which can be practically used at a room temperature.

Abstract: A process for preparing an .alpha.-L-aspartyl-L-phenylalanine methyl ester which comprises the steps of reacting formyl-L-aspartic anhydride with L-phenylalanine in the presence of water at a high pH, to produce formyl-.alpha.-L-aspartyl-L-phenylalanine; removing the formyl group from the formyl-.alpha.-L-aspartyl-L-phenylalanine and esterifying the resultant compound with methanol and hydrogen chloride to produce the hydrogen chloride salt of .alpha.-L-aspartyl-L-phenylalanine methyl ester; neutralizing the hydrogen chloride salt of .alpha.-L-aspartyl-L-phenylalanine methyl ester; and filtering the neutralized solution to produce .alpha.-L-aspartyl-L-phenylalanine methyl ester.